The situation in Yemen looks to be a very dangerous and unstabling scenario with likely world-wide ramifications. This latest scenario was initiated 3 days ago and already has escalated into some very worrying news - and worsening daily:

A Saudi-led coalition carried out air strikes on the Yemeni capital Sanaa for a third night on Friday

Yemen President Abdrabbuh Mansour Hadi has accused Iran of destabilising the country, calling Houthi rebels the "stooges of Iran".

Meanwhile, Saudi Arabia says military intervention in Yemen will continue until the country is "stable and safe".

The move comes after a third night of airstrikes by a Saudi-led coalition hit cities across the country.

The conflict has been described by correspondents as a proxy war between Sunni Arab nations and Shia Iran.

President Hadi was speaking at an Arab League summit in Egypt to discuss the crisis, days after having to flee Yemen as rebels advanced on his stronghold of Aden.

Arab military force

The Saudi-led Operation Decisive Storm has the support of several Arab League members. It was sparked by Wednesday's rebel advance towards Aden, in southern Yemen - a push that air strikes have failed to stop.

With no sign of an end to the current military campaign, the Yemen president said that military intervention must continue until the Houthi rebels surrendered.

At the summit in Sharm el-Sheikh, Egyptian President Abdel Fattah al-Sisi called for the creation of a joint Arab military force to deal with "unprecedented threats" in the region.

Egypt has already pledged planes, warships and troops to the coalition. President Sisi referred to ""foreign interference" in Yemen - a coded reference to Iran, according to analysts.

On Friday night, Yemeni Foreign Minister Riad Yassin said there was an "arrangement" for ground troops of the Saudi-led coalition to deploy in Yemen.

Iran is alleged to be supporting the Houthis. The rebels officially deny this, but senior figures have been seen in Iran's holy city of Qom and there are unconfirmed reports of Iranian pilots flying Yemeni planes, reports the BBC's security correspondent Frank Gardner.

Speaking after President Hadi, United Nations Secretary General Ban Ki-moon called for negotiations to avoid "a long, drawn-out conflict".

"Unjustified aggression"

The Houthis have said their aim is to replace Mr Hadi's government, which they accuse of being corrupt.

Rebel leader Abdul Malik al-Houthi has vowed not to surrender to what he called the "unjustified aggression".

Iran has also criticised the Saudi intervention. "They have to stop," Iranian Foreign Minister Mohammad Javad Zarif said on Friday.

Saudi evacuation

Hours before the summit began, the Saudi navy evacuated dozens of its own and foreign diplomats from Aden as airstrikes failed to slow the rebel advance.

US President Barack Obama has reaffirmed his support for the operation. On Friday the US military rescued two Saudi pilots who ejected from their F-15 fighter jet over the Gulf of Aden, a US defence official said.

Screaming and crying

Residents reported an intense overnight bombardment of both Aden and the capital Sanaa, in the third day of airstrikes.

Since the air campaign began, at least 39 civilians - including six children under the age of 10 - have been killed, Yemen health ministry officials say.

A resident of Sanaa, Mohammed al-Jabahi, told AFP news agency that his family had spent the night in fear.

"Whenever a plane flies over our home and is met by anti-aircraft gunfire, my three children run to a corner and start screaming and crying," he said.

Houthi rebels have taken to the streets to defy Saudi led airstrikes

Yemen - Who is fighting whom?

The Houthis: Zaidi Shia-led rebels from the north, who seized control of Sanaa last year and have since been expanding their control

President Hadi: Fled to Saudi Arabia after rebel forces advanced on his stronghold in the southern city of Aden

Al-Qaeda in the Arabian Peninsula: Seen by the US as the most dangerous offshoot of al-Qaeda, AQAP opposes both the Houthis and President Hadi.

Islamic State: A Yemeni affiliate of IS has recently emerged, which seeks to eclipse AQAP

The decision by King Salman bin Abdulaziz al-Saud to order airstrikes against Houthi rebels is the most important foreign policy decision undertaken by the House of Saud since revolutions swept across the Arab world four years ago.

Reports indicate that the Saudis have mobilised as many as 150,000 troops to their southern border primarily for the purpose of homeland defence, but also clearly to afford the kingdom the option to stage a ground war should it so choose.

Whether such a ground intervention will come is as yet unclear, but the kingdom has decisively played its hand against the Houthis, and in the process dramatically upped the stakes in a regional power struggle with Iran which now involves Lebanon, Syria, Iraq, Bahrain and Yemen.

Saudi Arabia's major foreign policy decisions are usually the product of consensus among top princes, and the Yemen operation is no exception.

Indeed, had the previous King Abdullah still been alive he would almost certainly have come to the same conclusion.

Ordering airstrikes was a momentous foreign policy decision for King Salman

Nevertheless, this is a real test for the new king, and failure to achieve Saudi Arabia's aim of reinstating ousted President Abdrabbuh Mansour Hadi would be an embarrassing defeat.

Failure is not an option, in particular for the king's 34-year-old son Prince Mohammed bin Salman, who as minister of defence is serving in his first senior post in government.

The risks for the young man are great.

His cousin Prince Khalid bin Sultan bin Abdul Aziz al-Saud launched what is widely regarded as a failed operation in Yemen in 2009, and his career has never fully recovered, with the one-time shoo-in for minister of defence seeing his portfolio dim dramatically.

Although Prince Mohammed is secure in his post, the problems would begin if his aging father were to pass away - the Byzantine world of Saudi court politics would be unlikely to forgive a failed Yemeni operation.Prince Mohammed (right) received Mr Hadi in Saudi Arabia after the president fled Yemen

The young prince must ensure that he gets this right. The stakes are high.

It is unlikely that the kingdom is looking to involve itself in a protracted conflict.

Saudi troops marching into Yemen have found it tough going since 1934. Logistics and supply lines are hard to maintain, and Yemenis know their rugged terrain better than any foreigner.

Leverage

An extended occupation of the country would be disastrously costly both financially and in terms of lives, even if the Houthi insurgency was militarily defeated.

The question is what does Saudi Arabia seek to achieve through the use of military force.

Air strikes alone will not be enough to defeat the Houthis, and a long term military operation would stretch Saudi operating capacity thin.

Air strikes have targeted arms depots and the Houthi movement's leaders

The message from Riyadh also leaves no doubt that the Saudis seek a negotiated settlement in which President Hadi brings together Yemen's different constituencies, including the Houthis, to work out a fairer constitutional settlement.

This could include a fairer distribution of provinces, and possibly more autonomy for Yemen's south where agitation from separatists is growing larger by the day.

Additionally, it is important to understand whether Saudi Arabia seeks a solution in Yemen with the hope of affecting affairs elsewhere in the Arab world.

Could for example, a political deal in which the Houthis are on the backfoot in Sanaa be used as leverage against the Iranians in Syria to force President Bashar al-Assad to step down from power or allow greater Sunni political influence in Baghdad?

Iranian support

It is a long shot but given current regional dynamics the Saudis will be looking to push all of the pressure points they can get against Iran and its allies.

Iran's position on Yemen is also quite clear - it seeks a political solution in Yemen that does not involve long term conflict and in which its allies, the Houthis, are given a seat at the table.

But should this not be possible the hardliners in Tehran would like nothing more than to see the Saudis bogged down in a conflict that they cannot hope to win.

Although Iran's logistical and diplomatic support to the Houthis has been fairly limited, the level of the military response in Riyadh shows that the Iranians clearly have the Saudis rattled, for far less time and money than the Saudis expended in Syria to force Iran's hand.Houthis have vowed to fight on in the face of the Saudi-led campaign

In a conflict in which no side has indicated that it seeks anything other than a diplomatic solution, it seems odd that the risk for protracted conflict is so high.

However, the Houthis do not look to be backing down.

Houthi leader Abdul Malik al-Houthi indicated in a televised address shortly after the airstrikes began that all foreign invaders would be resisted.

Danger

The hope is that while the Houthis talk tough, that they understand that they are not welcomed by the local population and by tribal confederations across large swathes of Yemen, particularly in the north east and south west of the country.

So whether the Houthis like it or not, they will have to compromise.

The danger is that Yemen could descend into a fractured and long term war, which drags in the region's main players and gives additional space for al-Qaeda and Islamic State (IS) to exploit.

To avoid such a scenario, much depends on the ability of all parties to come out of this conflict without appearing to have lost face.

Because, if the Syria example is anything to go by, a war will continue indefinitely until all parties feel they have more to gain from talking and compromising than they do from fighting.